Source:

https://docs.typo3.org/c/typo3/cms-core/master/en-us/Changelog/9.0/Important-82445-MigratePagesLanguageOverlayIntoPages.html

Description:

The functionality of “pages_language_overlay” has been migrated into “pages”.

An upgrade wizard is in place to migrate all existing data into the “pages” database table.

All relations directly to “pages_language_overlay” are migrated to the newly created “pages” records as well.